feat: 审计修复 Phase 6-7 — SSE 推送/工作流补全/消息群发/前端收尾

Phase 6 功能补全:
- P1-3: 消息 SSE 实时推送端点 + 前端 EventSource 连接
- P1-6: ServiceTask HTTP 调用能力 (reqwest GET/POST)
- P1-7: user.deleted 事件处理 — 终止相关流程实例
- P1-8: 任务认领 (claim) 端点 + handler
- P1-9: 超时检查器发布 task.timeout 事件
- P1-15: 组织/部门名称唯一性校验 (create + update)
- P1-18: 消息群发 fan-out (role/department/all 批量投递)

Phase 7 P3-P4 收尾:
- PluginAdmin purge 按钮状态修复
- ChangePassword 最小 8 字符 + 新旧密码不同验证
- AuditLogViewer 用户名缓存 + 扩展资源类型
- InstanceMonitor 通过 definition 缓存解析 node_name
- NotificationPreferences DND 时间范围校验

Cargo.lock

@@ -1442,15 +1442,18 @@ name = "erp-message"
 version = "0.1.0"
 dependencies = [
  "anyhow",
+ "async-stream",
  "async-trait",
  "axum",
  "chrono",
  "erp-core",
+ "futures",
  "sea-orm",
  "serde",
  "serde_json",
  "thiserror 2.0.18",
  "tokio",
+ "tokio-stream",
  "tracing",
  "utoipa",
  "uuid",
@@ -1587,6 +1590,7 @@ dependencies = [
  "axum",
  "chrono",
  "erp-core",
+ "reqwest",
  "sea-orm",
  "serde",
  "serde_json",